There is an increasing demand for the most accurate possible three-dimensional representation of the appearance and pattern of vessels in parts of the body, in particular of arteries and veins, for diagnostic purposes within the field of vascular diseases and the therapy thereof. The examination of cerebral aneurysms represents an important field of application, this also includes an analysis and optimal representation for defining the aneurysm neck using topographical relations with adjacent vessels. Angiographs are also carried out on different parts of the body, in order to determine arteriosclerotic changes or deformities. The introduction of computer-aided rotation angiography, which reconstructs three-dimensional representations with an equal resolution from the projection raw data, achieves a technical breakthrough within the field of diagnostics. The so-called C-arm angiographs form here the prior art, in which an x-ray source and an x-ray detector arranged on a C-arm and opposite thereto, are rotated about the part of the body of a patient to be examined in an arc encompassing approximately 200° and between 50 and 500 x-ray images are recorded here and digitally stored. A three-dimensional model of the x-rayed part of the body can be calculated from x-ray images recorded from different projection angles. The conventional 3D angiography nevertheless fails to ensure an adequately clear separation between the arterial and venous vascular systems, by virtue of the recording times and the dynamics of the contrast agent propagation.
With the afore-described three-dimensional vascular representation, a so-called mask pass and a filler pass are recorded. During the “mask pass”, the C-arm rotates about the part of the body of the patient or the whole patient and records a first sequence of x-ray images without contrasting over the predetermined angular range. A contrast agent is then injected into the vessel of interest and with another C-arm rotation, the so-called “filler pass”, a second sequence of x-ray images is recorded. The two sequences are now subtracted from each other such that only the contrasted vessels (i.e. containing contrast agent) can still be seen in the result. These are now reconstructed to form a three-dimensional image data record using a 3D reconstruction method. Alternatively, masks and filler pass sequences can also be reconstructed separately and the resulting three-dimensional data records are subtracted from one another.
The 3D angiography method according to the prior art generally provides a three-dimensional image data record, which represents both a part of the arterial vascular system as well also as parts of the venous vascular system. The reason for this flaw in current angiography systems can be attributed to the rotation time of the C-arm of 5 s being significantly longer than the arterial phase of the vascular contrasting, which only lasts 2 to 3 seconds. The contrast agent then permeates over the conventional capillary paths into the venous vascular system so that a venous phase of the vascular contrasting is indicated after the arterial phase has passed, said vascular contrasting being characterized in a subsequent part of the rotation of the tomographs, thereby resulting in a three-dimensional mixed structure of arteries and veins.
DE 102 41 184 A1 discloses a method for generating a volume data record of an object using a first and a second x-ray system, with which a first series of 2D projections of the object is recorded with the first x-ray system at projection angles which differ from one another, with the first x-ray system being rotated about an axis and scanning a first angular range, and with which a second series of 2D projections of the object are essentially recorded at the same time using the second x-ray system at different projection angles from one another, with the second x-ray system being rotated about an axis and scanning a second angular range which differs from the first angular range.